In a number of power tools, particularly gasoline powered string trimmers or brush cutters, with a power unit at the handle portion of the tool and a working implement remote from the power head, a mechanism must be provided for properly transmitting power from the power head to the working implement. This is accomplished utilizing a drive shaft tube which contains a flexible shaft, the flexible shaft interconnecting a drive shaft portion from the power head, and a drive shaft portion from the working implement. Conventional mechanisms for clamping the drive shaft tube to a trimmer head (the power head or working implement head) have been relatively expensive and have had less than desired durability.
A typical manner of attaching the drive tube to the power head or working implement head is an external clamp, such as a conventional hose clamp. Another common alternative is to form the power head or working implement head as a split housing, with one or more screws deforming the housing and clamping the tube. The split housing arrangement can result in high force concentrations, which may result in fracturing of the tube, especially when it is thin-walled. A split housing arrangement is also relatively expensive, and the hose clamp arrangement does not have the desired durability or aesthetic appeal.
According to the present invention, a clamping mechanism is provided for clamping two tubular components together, which clamping mechanism is particularly adapted for use with string trimmers or brush cutters, or like power tools. The clamping mechanism according to the present invention is relatively inexpensive, yet is very durable, providing uniform clamping pressure over substantially the entire length of the clamp at the points of contact between the clamp, drive tube, and housing, so that undesired force concentrations are avoided. Also, the clamping mechanism according to the present invention has good aesthetic appeal.
According to one aspect of the present invention, there is provided a string trimmer comprising: A power source. A trimmer head including a first one-piece tubular housing portion having an inner surface. A flexible shaft for operatively interconnecting said power source and said trimmer head. A second tubular housing portion containing said flexible shaft therewithin, said second tubular housing portion having an outer surface of generally the same cross-sectional shape and area as said first housing portion inner surface, and having an inner surface; and means for clamping said first and second housing portions together so that the outer surface of said second housing portion engages the inner surface of said first housing portion, while said first and second shaft portions are in operative association with each other. The clamping means comprise: A plurality of inner clamping components, each having an outer surface having a circumferential extent less than the circumferential extent of the inner surface of said second housing portion, and said inner clamping component outer surfaces collectively having a circumferential extent substantially equal to the circumferential extent of said second tube inner surface; and a plurality of outer clamping components cooperating with said first housing and said inner clamping components to provide a clamping force holding said second housing outer surface into clamping engagement with said first housing inner surface with a generally uniform clamping force over the area of interengagement between said first housing inner surface and second housing outer surface.
While for clarity of presentation the invention is described with reference to a gasoline powered string trimmer, or the like, it is to be understood that the clamping mechanism according to the invention is also utilizable with a wide variety of other power tools, or in other environments where uniform clamping pressure between concentric tubular portions is desirable. It is the primary object of the present invention to provide a clamping mechanism for clamping concentric tubular portions together with a uniform clamping force. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.